Sampling device



Nov. 5, 1968 F. P. AUGER 3,403,869

- SAMPLING DEVICE Filed Oct. 13, 1966 2 Sheets-Sheet 1 I I I I I '2 I za FIG. I h

avdlLmluod,g

n'ronm' Nov. 5, 1968 F. P. AUGER 3,408,869

SAMPLING DEVICE Filed Oct. 13, 1966 2 Sheets-Sheet 2 I I o N ATTORNEY;

United States atent O ice 3,408,869 SAMPLING DEVICE Frank Pawley Auger,Surbiton, Surrey, England, assignor to The Distillers Company Limited,Edinburgh, Scotland, a British company Filed Oct. 13, 1966, Ser. No.586,482 11 Claims. (Cl. 73-4215) This invention relates to samplingdevices and in particular to devices for sampling a stream of fluid.

In order to monitor, for example, the vapour within the outlet pipe of achemical reactor, where equilibrium conditions may be considered toobtain for all practical purposes, a part of the reactor output vapourcan be diverted through valves to a receiver. If the receiver is ananalysis instrument, such as a gas chromatograph, it is desirable that areproducible sample be taken each time. For this purpose the valves arenormally situated in a sampling pipe which is in parallel with the mainreactor outlet pipe and through which reactor output vapour iscontinuously passed except momentarily during switching. Thisarrangement allows a reproducible sample to be taken as required byappropriate switching of the valves. This sample can be transferred fromthe sampling pipe to the receiver by a stream of a carrier gas, forexample, helium.

A particularly useful type of valve for this purpose is a multi-positionvalve comprising a rotor face-to-face with a stator; the rotor having atleast one channel cut in its face, and the stator having a plurality ofports cut in its face. Valves of this type have good sealingcharacteristics, thus providing reproducibility of sample size. However,when dealing with vapours above about 200 C., the lubrication andsealing of such a valve becomes difficult, since under such conditionslubricants are liable to carbonize and the elevated temperatures maylead to distortion of the valve faces and corrosion problems.

It is an object of the present invention to provide apparatus suitablefor sampling a stream of fluid at high temperature which enablesreproducible samples to be withdrawn from a reactor gas stream withoutrelying on high precision mechanical valves to define the sample.

According to the present invention, there is provided apparatus whichcomprises an elongated vessel, provided with an inlet at one extremityand an outlet at the other extremity, flow restricting devices adjacentthe said inlet and outlet, ports adjacent the said flow restrictingdevices and a third port situated between the aforesaid ports.

In a preferred embodiment the apparatus comprises two similar coiledtubes connected by a T-piece which thereby provides a central port atright angles to the flow direction of the vapour to be sampled. Theapparatus is further provided with T-pieces at the free ends of thecoiled tubes, thereby providing ports again at right angles to thesample flow. Flow restricting devices are also provided adjacent theinlet and outlet. They should be situated between the outlet, or inlet,and its nearest port.

In operation, the device is connected, for example, as a by-pass to astream of reactor output vapour and carrier gas which is inert to thecomponents of the reactant output vapour under the prevailing conditionsis passed continuously into the apparatus through all three ports atvery low fiow rate, so that no diffusion of reactor vapour occursthrough the ports. Passage of reactor vapour is allowed continuouslythrough the coiled tubes and the reactor vapour is diluted only with asmall but constant amount of carrier gas. When a sample is required tobe withdrawn, carrier gas at high pressure is introduced via the portssituated at the inlet and outlet ends, and simultaneously the slow feedat the central port is interrupted. On entering the sample device thehigh pressure Patented Nov. 5, 1968 carrier gas splits into two streams,one directed towards the centre of the device and the other directedaway from it. Thus, at each end of the device the stream ofreactorvapour is interrupted by the flow of high pressure carrier gas, andswept either toward or away from the central port. The sample istherefore defined by the points of entry of high pressure gas. In orderto obtain a definite break in the vapour stream it is important that theflow of high pressure carrier gas should take place in each directionfrom the ports and therefore the flow restricting devices must not atany time close the tubes entirely. The sample of reactor vapour is sweptout via the central port and the slow bleed of carrier gas through thethree ports is then resumed.

The restricting devices may, for example, be simple constrictions orother fixed mechanical contrivances designed to provide a back pressure.Alternatively they may be valves which need only be of a relativelycrude type. It is particularly preferred however, to use a valvearranged to provide a higher degree of restriction than normal duringthe actual sampling operation. In one such embodiment a bellows valve isconnected to the source of supply of high pressure gas. Adjacent thebellows valve is provided a small aperture in the wall of the sample vessel. When high pressure gas is switched on, the bellows valve inflatesand closes the tube, thereby creating a back pressure, while restrictedflow of gas is permitted through the aperture.

The streams of carrier gas may suitably be introduced into the device bymeans of a multi-position valve of the type referred to above. Thesample may be removed from the device by way of such a valve.

By means of the present invention the multi-position valve or valvesneed only receive hot reactor vapour during the actual samplingoperation and therefore, bearing in mind their relatively large mass,the valves remain comparatively cool and are not maintained at the highreactor gas temperature.

The invention will now be described with reference to the accompanyingdiagrammatic drawings in which FIGURE 1 represents a fiow diagram of avapour sampling device of the invention.

FIGURE 2 represents a flow diagram of a vapour sampling device of theinvention, connected in an operative position.

The device shown in FIGURE 1 of the drawings is a simple embodiment ofthe invention which can be used, for example, in parallel with theoutput pipe of a chemical reactor. The device shown comprises a sampletube divided into two substantially equal portions V and V A T-piece Xconnects V and V and other T-pieces, Y, Z, are at the ends of V and Vremote from X. Constrictions F, G are located in the arms of D, E ofT-pieces Y, Z respectively.

In use, a stream of the vapour to be sampled flows through the devicefrom D to E, through F, Y, V X, V Z and G in that order. Diffusion ofthe vapour up side-arms A, B, C of the T-pieces Y, X, Z is prevented byallowing a small amount of a suitable carrier gas, for example helium,to bleed into the vapour stream at a suitable rate through the side-armsA, B, C. Thus the vapour in the sample tube is admixed with a smallamount of the carrier gas.

On taking a sample, side-arms A and C are connected to a high pressuresource of carrier gas. Simultaneously, side-arm B is connected to asample receiver (not shown), for example a gas chromatograph. The highpressure gas at Y and Z divides the vapour stream flowing through thedevice and pushes the vapour in V and V out through the side-arm B. Theconstrictions F, G restrict the flow of vapour and gas outwardly, thusproviding the necessary pressure differential to drive the sample outthrough side-arm B. When all the samplehas been driven into the samplereceiver, side-arms A, B and C are again connected to their sources oflow pressure carrier gas and the carrier gas contained within thevolumes V and V is swept out by the vapour stream through the device.

The device in FIG. 2 is represented as being within the outlet pipe of achemical reactor, indicated by the broken lines, so that vapour flowsthrough the device. The vapour flow through the device can be assistedby placing the device in parallel with a restrictor plate in order toaugment a pressure difference between the inlet and outlet of thedevice. The device comprises two bellows 1, 2 connected by sample coils3, 4. The ends of the coils 3, 4 adjacent the valves 1, 2 are connectedby lines 5, 6 to a line 7 which is connected to a port 10 of a ten-portmultiposition distributor valve 8. The junction of the sample coils 3, 4is connected by line 9 to a port 17 of the tenport valve 8. The bellowsof the bellows valves 1, 2 are connected by lines 20, 21 to a line 22which, in turn, is connected to a port 13 of the ten-port valve. Betweenthe valves 1, 2 and the lines 5, 6 there are apertures 23, 24respectively, which permit restricted flow between the sample device andthe outlet pipe of the chemical reactor. In a preferred alternativeembodiment (not shown) the restricted flow apertures are built into thebellows valves. The remaining ports of the ten-port valve 8 areconnected as follows:

Port 18 to a chromatograph column 25.

Ports 19, 11 and 16 to flow-controllers 28, 27, 26 respectively.

Port is blanked off.

Port 12 is open to the atmosphere.

Port 14 is connected by line 29 to a pressure regulator 30, to which theflow controllers 26, 27 and 28 are also connected.

A pre-column 31 is an optional feature which may be inserted in the line9.

The pressure regulator is connected to a source of a suitable carriergas which may be for sample, hydro gen, nitrogen, carbon dioxide or anoble gas, as required by the nature of the vapour to be sampled.

The connections between the ports of the ten-port valve 8 are made asindicated by the full lines in the steady state, and as indicated by thedotted lines when a sample is being taken.

In the steady state, the outlet vapour of the chemical reactor flowsthrough the sample coils 3, 4. Carrier gas flows slowly, throughcontroller 26, by way of port 16, port 17 and line 9, to the juncture ofthe sample coils 3, 4 at such a rate that there is no appreciablediffusion of vapour up line 9. Carrier gas also flows through controller27 by way of port 11, port 10 and line 7 to lines 5 and 6. The rate offlow of carrier gas in lines 5 and 6 is such that there is noappreciable diffusion of vapour up lines 5 and 6. Carrier gas at asomewhat higher pressure flows through controller 28 by way of port 19and port 18 to the column 25.

To take a sample of the vapour flowing through the coils 3, 4 the valve8 is rotated so that the connections indicated by the dotted lines aremade. In this position, carrier gas from controller 28 flows by way ofport 19, port 10 and line 7 to lines 5 and 6. At the end of line 6remote from line 7 the carrier gas stream divides into two parts, partpushing the vapour sample within coil 4 up line 9 and part pushingtowards bellows valve 2. Bellows valve 2, having been connected to asource of carrier gas at high pressure, namely line 29, will then be inthe closed position, as shown by the dotted lines, and the vapourbetween the valve 2 and the end of line 6 will slowly leak out into thereactor outlet pipe through the restricted flow aperture 24. A similarcourse of events occurs at the other end of the device, and a vapoursample flows up line 9 through the ports 17 and 18 onto the column 25.

When the sample is to be fed to a chromatographic column, it isdesirable that condensation of vapour should not occur in the valve 8,as this would give rise to badly shaped peaks on a recorder. To avoidthis a pre-column 31 may be inserted in the line 9 between the actualsampling device and the valve. The pre-column is packed with a materialin which the vapour components of the sample are soluble so that thepartial vapour pressures of the components are reduced before they reachthe valve. This reduction in vapour pressure reduces the possibility ofcondensation occurring when hot vapours meet relatively cool valveparts.

When the whole of the vapour contained within the coils 3, 4 has passedthrough the port 18, the valve 8 is returned to the steady stateposition. The bellows valves 1, 2 open since they are vented to theatmosphere by the connection of the port 13 to port 12, and carrier gaswithin the coils 3, 4 is rapidly flushed out by the flow of vapourtherethrough.

In order that the opening and shutting of the various valves shall occurin the correct sequence it may be advantageous to introduce pneumaticdelays at various points in the control system described above.

I claim:

1. Apparatus suitable for sampling a streamof fluid, which comprises anelongated vessel having an inlet at one extremity, an outlet at theother extremity, flow restricting devices adjacent the inlet and outlet,ports adjacent the said flow restricting devices and a third portsituated between the aforesaid ports.

2. Apparatus according to claim 1 wherein the three ports are providedby tubular T-pieces and the third port is separated from the other portsby two coiled tubes.

3. Apparatus according to claim 1 wherein the flow restricting devicesare fixed constrictions.

4. Apparatus according to claim 1 wherein the flow restricting devicesare valves which may be adjusted to provide an increased degree ofconstriction during the sampling operation.

5. Apparatus according to claim 1 wherein the flow restricting deviceseach comprise a bellows valve and an aperture in the wall of theelongated vessel adjacent the bellows valve, whereby during samplingoperations the bellows may be inflated to close the inlet and outlet ofthe elongated vessel whilst restricted flow of fluid is permitted viathe aperture.

6. A process for obtaining samples from a stream of fluid whichcomprises passing the fluid through an elongated vessel having a flowrestricting device at each extremity, ports adjacent the said flowrestricting devices and also a third port situated between the said twoports, passing carrier gas into the vessel via the ports at a velocitysufficient to prevent diffusion of the fluid to be sampled into theports, and, when a sample is required, introducing carrier gas at highpressure via the ports adjacent the inlet and outlet while interruptingthe flow of carrier gas at the third port, whereby the sample fluidbetween the ports adjacent the inlet and outlet is swept out through thethird port, while the sample fluid not located between the said ports isswept out of the vessel past the flow restricting devices.

7. The process according to claim 6 wherein the flow restricting devicesare provided as fixed constrictions.

8. The process according to claim 6 wherein the flow restricting devicesare provided as adjustable valves.

9. The process according to claim 6 wheerin the flow restricting devicecomprises a bellows valve and an aperture in the wall of the elongatedvessel adjacent the said bellows valve, wherein the bellows valve is soarranged that when high pressure carrier gas is supplied to the twoports for sampling purposes it is also supplied to the bel- 5 lowsvalve, thereby closing the said valve and thus allowing escape ofcarrier gas and fluid only by the Said aperture.

10. The process according to claim 6 wherein the carrier gas ishydrogen, nitrogen, carbon dioxide or a noble gas.

11. The process according to claim 6 in which the apparatus is situatedin a sample pipe which is in parallel with the main outlet pipe of achemical reactor.

References Cited UNITED STATES PATENTS Webber 73-421.5

Riordan 13781.5 Barrett 55--67 Roof 73-422 X S. CLEMENT SWISHER, ActingPrimary Examiner.

1. APPARATUS SUITABLE FOR SAMPLING A STREAM OF FLUID, WHICH COMPRISES ANELONGATED VESSEL HAVING AN INLET AT ONE EXTREMITY, AN OUTLET AT THEOTHER EXTREMITY, FLOW RESTRICTING DEVICES ADJACENT THE INLET AND OUTLET,PORTS ADJACENT THE SAID FLOW RESTRICTING DEVICES AND A THIRD PORTSITUATED BETWEEN THE AFORESAID PORTS.